1. Field of the Invention
This invention relates to a hard coating as a surface coating material for cutting tools used in machining methods such as milling, cutting and drilling, or as a surface coating for wear resistant material in parts requiring high hardness such as molds, bearings, dies, and rollers, or as a surface coating material for heat resistant and corrosion resistant members used in molding machines such as screws and cylinders. This invention further relates to a hard coating coated member having excellent wear resistance due to the hard coating thereon.
2. Description of the Related Art
In cutting tools such as high speed and carbide cutting tools which require high wear resistance, hard coatings consisting of TiN and TiC are formed on the surface of cutting tools in order to improve the wear resistance.
In comparing the wear resistance of the above TiN and TiC, TiN has an oxidation resistance superior to TiC at high temperature and demonstrates good wear resistance to crater abrasion occurring on the cutting tool surface from cutting or frictional heat generated during cutting. The TiN also demonstrates superior adhesive properties to the substrate material. The TiC on the other hand, has higher hardness than the TiN and demonstrates high durability with respect to flank wear where the tool flank surface contacts the work piece.
However even in TiN which has superior oxidation resistance, the temperature at which oxidation starts is at most about 600.degree. C. and even in high hardness TiC, the Vickers hardness is at most about 2,000, therefore, in either case further improvement is needed.
At which point, for example in Japanese Patent Laid-open No. 2-194159, in an effort to improve the oxidation resistance and hardness of the TiN and TiC, nitrogen compounds of Al and Ti and carbon-nitrogen compounds with aluminum replacing a portion of the Ti (titanium) was used {hereafter shown by (Al, Ti) (C,N)}. This improved the oxidation temperature to approximately 800.degree. C. and the Vickers hardness to about 2500.
The inventors of this patent completed patent application for a hard coating demonstrating excellent wear resistance, good resistance to oxidation and high hardness, by means of replacing a portion of the elements with other elements and utilizing an aluminum-titanium-nitride compound as a base. For instance the (Al, Ti) (B,N) in Japanese Patent Laid-open No. 4-26756 had an oxidation temperature of approximately 800.degree. C. and a Vickers hardness of 3400. Also the (Al, Ti, Si) (C,N) film (Japanese Patent Application No. 6-100154) had an oxidation temperature of approximately 1000.degree. C. and a Vickers hardness of 3100.
However it is necessary to develop a hard coating having even better wear resistance for applications in fields requiring an even higher performance such as in cutting tools.